Alkyl-1-thioglycosides having a long alkyl or fatty acid chain and their oxygenated analogs are known for their surfactant properties and are used as surfactants or detergents. An important characteristic of these families of glucide derivatives is the ability of the hydrophobic and hydrophilic functional groups therein to simultaneously combine on the same molecule. This characteristic allows these compounds to form monomolecular layers at the interfaces between immiscible solvents and micelles when the concentration of the micelles in solution exceeds a limit value known as the critical micelle concentration (CMC). This physical-chemical behavior is the cause of exceedingly significant, as well as diverse, applications of the surfactants as wetting agents, dispersants, emulsifiers, and, more generally, solubilizers. The surfactants also are known for their thermotropic and lysotropic properties of liquid crystals.
The alkyl glycosides having a fatty acid chain and alkyl-1-thioglycosides constitute an especially significant class of detergents because, being nonionic, their CMC and hence many of their desirable properties do not depend on the presence of a compensating ion. The generally high CMC value of these materials allows for easy and rapid elimination of the compounds by dialysis. These features in particular have led to their preferential use in biochemistry as solubilizers, in the extraction and reconstitution of membrane proteins, and their use as amphiphile derivatives which can act as a denaturant for complex and unstable biological structures. The fatty acid chain alkyl-1-thioglycosides also are of interest in relation to their alkyl glycoside analogs since the analogs are insensitive to most of the glycosidase enzymes which are present in biological media, as shown by the results published in Biochem. J., 222 (1984) 829. Regarding the biochemical applications reported to date in the literature, only the 1,2-transanomers of the alkyl-1-thioglycosides have been put to use (see for instance Chem. Pharm. Bull., 33, No. 2 (1985), 503).
Generally, alkyl-1-thioglycosides are prepared by reacting an alkyl halide with an o-acetylated 1-thioglycose, as disclosed in Japanese Patent No. 61-7288. Another method recently suggested (Tetrahedron Lett., 29 (1988) 4293) makes use of the principle of the radical addition of an alkene onto this same derivative of 1-thioglycose in the presence of azobis-(isobutyronitrile). Such procedures, however, are time-consuming because they require at least four stages and employ costly reagents. Furthermore, these procedures lead solely to the 1,2-trans anomer of alkyl-1-thioglycopyranoside because the precursor acyl-1-thioglycose has the same configuration based on its synthesis. Accordingly, at this time only fatty acid chain alkyl-1-thioglycopyranosides of .beta.-D anomerism in the series of glucopyranose, galactopyranose and xylopyranose have been described, or with regard to the .alpha.-D form, mannopyranose.
The fatty acid chain alkyl glycosides are generally prepared by trans-acetylation in the presence of an acid catalyst in the manner as described in German Patent Application Nos. DE-A-1,905,523 and DE-A-1,943,689. The starting compounds are usually a lower glycoside alcohol or a mixture of a glycoside and a lower alcohol and a fatty alcohol. A related procedure to the Koenigs-Knorr reaction, which involves the action of a long chain alcohol on a peracetylated glycosyl halide in the presence of silver salts, has also been suggested by Koeltzow et al in J. Am. Oil Chem Soc., 61 (1984) 1651. This latter procedure also results in the .beta. anomers of cellobiose, maltose and maltotriose.
Applicant's PCT application WO-A-8600906 describes a synthesis of fatty alcohol alkyl glycosides by reacting a fatty alcohol with an aldose, an aldoside or a polyaldoside in a solvent and reagent consisting of a mixture of dioxane/hydrogen fluoride or sulfur dioxide/hydrogen fluoride resulting in a yield of about 30%. This procedure, however, is not usable for synthesizing alkyl oligosaccharides because the reaction conditions result in fluorolysis of the oxygenated interoside bonds. Lower alcohol alkyl glycosides can be synthesized with good yields in the manner according to WO-A-8600906 by reacting an alcohol with an aldose, an aldoside or a polyaldoside in a solvent and reagent consisting of hydrogen fluoride. However, the quantity of alcohol used is high and the molar ratio of alcohol to the monosaccharide equivalent is advantageously about 20. Further, the lower alkyl oligosaccharides again are precluded for the aforementioned reasons.